Sampo SS2020 Power supply problem

[MurrayT]

Hi All. I have an Sampo SS2020 Oscilloscope that has a large downward pulses  at 100Hz on the 140V and 260V lines. The voltages read low ie 140 reads about 110 and the spikes go down from 110 by about 30V on the 140V line. The spike shape is not a sharp one but the like the lower 10% negative portion of a sine wave,  the bottom part is sort of rounded. It is definitely a spike and not the usual ripple seen on power rails on other devices. The best I could do so far is,  I have checked all the"R"s and a simple check of the "C"s (ie continuity test shows a rising voltage). The bridge rectifiers check OK with a multimeter diode tester.  Seems to me it might be electrolytic ESR problems BUT the fault came on suddenly. Any suggestion gratefully received.

[shakalnokturn]

Most probably some of the larger capacitors on the power supply are bad.
Your method for testing them is not telling you enough.